Purpose: To assess the normal range of cerebral ventricular atrial diameters during the second and third trimesters of pregnancy.
Materials and methods: The transverse diameter of the atrium of the lateral ventricle was prospectively measured in 739 consecutive antenatal ultrasound examinations by positioning electronic calipers on the luminal margins of the ventricular wall, perpendicular to the long axis of the ventricle.
Results: The mean ventricular atrial diameter for the combined group of all 739 studies was 5.4 mm +/- 1.2 (standard deviation). The transverse diameter of the ventricular atrium did not progressively increase with advancing gestational age. All fetuses younger than 17 menstrual weeks had ventricular atrial diameters less than 8 mm. Four fetuses had ventricular diameters of 10 mm or greater.
Conclusion: A reasonable upper limit of normal for transverse atrial diameter for gestational age of 25 weeks and above appears to be 10 mm. Prior to 25 weeks, diameters over 8 mm are unusual in the healthy fetus and signal the need for a detailed evaluation of fetal anatomy.